Battery stack with distributed control of cells driving events

ABSTRACT

Embodiments of the present invention relate to a battery stack controller system. The system may include a plurality of battery cell stages with cell controller systems (as described above with respect to the first embodiment). The system may also include a stack controller to send charge/discharge commands to the battery stack via a communication network. The stack controller may send the commands to the battery stack based on the requirements of a load or the state of the battery cell stages. The battery cell stages may either comply with the commands or send the commands to neighboring cells via the communication network.

RELATED APPLICATIONS

This application claims priority to U.S. Patent Application Ser. No.61/862,835 filed on Aug. 6, 2013, the content of which is incorporatedherein in its entirety.

BACKGROUND

The present invention relates to battery stack control systems.

Battery stacks include a plurality of individual “cells” are arranged inseries in order to build a battery stack having a desired outputvoltage. A large number of cells may be arranged in series such that,for example, the total potential difference developed across the batterystack is in the order of a several hundred volts. Each cell typicallyonly has a potential difference of a few volts (e.g., 3 volts) developedacross it. Battery stacks also include a switch control, which can beused to switch cells individually in and out of the stack and controlthe orientation of the cells (e.g., positive or negative orientation)within the stack to meet timing requirements. Battery stacks can be usedto generate time-varying outputs (e.g., sinusoidal signals) about aground value (e.g., +300 volts to −300 volts in a 100 cell stack).

Rechargeable battery stacks can be used in many applications. One suchapplication is the use of batteries in hybrid or fully electricvehicles. Hybrid and fully electric vehicles (HEV/EVs) are becomingincreasingly popular, therefore there is a need for more effective,efficient, and safe battery stack systems. Conventional battery stackssuffer from several problems during operation. For example, because eachof the cells in a battery stack discharges at a different rate, somecells may become too weak to supply voltage to a load. In such a case,the weakened cell can be permanently damaged if it is forced todischarge further and will eventually need to be replaced. Similarproblems occur when a fully charged cell is over-charged. Additionally,if a cell is damaged beyond repair, the stack needs to continue tooperate as required by the load. Conventional battery stacks fail toadequately account for such errors. Finally, when battery stacks areexposed to hazardous conditions (e.g., when they are submersed inwater), they can become flammable, causing serious safety issues. Thisproblem is specifically dangerous because there is a reasonablelikelihood that consumers will be in close proximity to battery cells.

Thus, there is a need for improved battery stack monitoring systems toaccount for the problems described above.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram of a single battery cell stage according to anembodiment of the present disclosure.

FIG. 2 is a state diagram of a local decision making process for eachbattery cell stage in a battery stack according to an embodiment of thepresent disclosure.

FIG. 3 is a state diagram of a local decision making process for eachbattery cell stage in a battery stack that is discharging according toan embodiment of the present disclosure.

FIG. 4 is a state diagram of a local decision making process for eachbattery cell stage in a battery stack that is charging according to anembodiment of the present disclosure.

FIG. 5 is a diagram of a battery stack according to an embodiment of thepresent disclosure.

FIG. 6 is a diagram of a battery stack with a transformer according toan embodiment of the present disclosure.

FIG. 7 is a diagram of a battery pack for a battery cell with anintegrated controller according to an embodiment of the presentdisclosure.

FIG. 8 is a diagram of a cell controller communication networkimplementing a leapfrogging protocol according to an embodiment of thepresent disclosure.

DETAILED DESCRIPTION

Embodiments of the present disclosure are directed to improved batterycells and battery stack controller systems. A first embodiment isdirected to a battery controller system. The control system may includea controller, sensors, transmitters, and receivers. The receivers mayreceive charge/discharge commands over a communication network. Thecontroller may determine the state or condition of the cell (e.g.,whether the cell is weak, strong, depleted, charged, etc.) using thesensor. Subsequently, the controller may determine whether the cell canfulfill the command or whether the command should be passed to aneighboring battery cell in a battery stack via the transmitters.

Another embodiment is directed to a battery stack controller system. Thesystem may include a plurality of battery cell stages with cellcontroller systems (as described above with respect to the firstembodiment). The system may also include a stack controller to sendcharge/discharge commands to the battery stack via a communicationnetwork. The stack controller may send the commands to the battery stackbased on the requirements of a load or the state of the battery cellstages. The battery cell stages may either comply with the commands orsend the commands to neighboring cells via the communication network.

A further embodiment is directed to an improved battery packagingdesign. The battery pack design may include a battery cell, a pluralityof transistors, and a controller. The transistors may be coupled to theterminals of the battery cell in an H-bridge configuration. Thecontroller may control the transistors to bypass the battery cell basedon the current flowing between the output terminals of the battery pack.In such a manner, the controller may prevent damage to the battery celland improve the overall safety of the battery pack in hazardousconditions.

Yet another embodiment is directed to a battery stack with aleapfrogging communication network. Each cell stage may include acontroller, a transmitter, and a pair of receivers. The cell stage inthe battery stack may be coupled to the closest two preceding batterycell stages in the stack. In this manner, each cell stage may be able todetermine if a fault is present in an immediately preceding cell stagein the stack by monitoring the first preceding cell stage and the secondpreceding cell stage. If discharge/charge commands transmitted by thesecond preceding cell stage are not reaching the battery cell stage atissue, the controller may determine that there is a fault in the firstpreceding cell stage and discharge/charge the cell stage based on thecommands transmitted by the second preceding cell stage.

FIG. 1 illustrates a cell stage 100 according to an embodiment of thepresent disclosure. The cell stage 100 may be one stage in a multi-stagebattery stack system (as shown in FIG. 3 below). As illustrated in FIG.1, the battery cell stage 100 may include a battery cell 110, a cellmonitor 120 coupled to respective ends of the battery cell 110, andswitches 132, 134, 136, and 138. The battery cell stage 100 maycommunicate with neighboring battery cell stages (not shown) in abattery stack via the upstream communication path 150 and the downstreamcommunication path 160.

The battery cell 110 may be a lead-acid, nickel-metal hydride (NiMH),lithium-ion (Li-ion), or other type of battery that may be integrated ina battery stack, including a plurality of battery cells, to providepower to drive a load (e.g., a motor).

The cell monitor 120 may include a controller 121, receivers 122 and123, transmitters 124 and 125, sensor(s) 126, and a memory 127. The cellmonitor 120 may make local decisions and switch-in or bypass theassociated battery cell 110 based on communications received on theupstream and downstream communication paths 150 and 160 and the localstate of the battery cell 110.

The controller 121 may include a microcontroller, a programmableprocessor, and/or a state machine. The controller 121 may make the localdecisions and switch-in/bypass the battery cell 110 based on thecondition of the battery cell 110. The receivers 122, 123 andtransmitters 124, 125 may be controlled by the controller 121 and mayreceive and transmit information via paths 150 and 160. In the upstream(or outbound) communication path 150, the receiver 122 may receive aPUSH/PULL command (described in more detail below) from a previous stagein the stack and transmitter 124 may transmit a PUSH/PULL command to anext stage in the stack. In the downstream (or inbound) communicationpath, receiver 123 may receive a PUSH/PULL command from a previousbattery stage in the stack and transmitter 125 may transmit a PUSH/PULLcommand to the next battery stage in the stack.

The sensor(s) 126 may determine a direction of current flow through thebattery cell 110, for example, whether current is flowing upwardly ordownwardly through a stack in which the cell 110 is a member. Thesensor(s) 126 may also measure operating parameters of the battery cell110, for example, charge level, health, temperature, fault status, orother conditions. The memory 127 may store data such as measurementstaken by the sensor(s) 126. The memory may also store logs of PUSH/PULLcommands received by the receivers 122 and 123. The data stored in thememory 127 may be accessed by the controller 121.

The switches 132, 134, 136, and 138 may facilitateswitching-in/bypassing of the battery cell 110 in the stack. Theswitches 132, 134, 136, and 138 may be controlled by cell controlcontroller 121. The switches 132-138 may be arranged in an H-bridgeconfiguration about the cell monitor 120 as shown in FIG. 1 and switchedin pairs. The switches 132-138 may be metal-oxide-semiconductorfield-effect transistors (MOSFETs) of sufficient size to serve as powertransistors or mechanical switches.

During operation, the battery cell stage 100 of FIG. 1 may receive andtransmit PUSH and PULL commands from adjacent cells in a battery stackvia the upstream and downstream communication paths. A PUSH command mayrepresent a command by an external controller to add positive voltage toan output of the stack in which the stage 100 belongs. The stage 100 mayrespond to a push command in a variety of ways, depending on operatingconditions at the stage 100. For example, if the stage 100 is configuredwith the battery cell 110 already pushing, it may continue to push andpass the PUSH command to another cell stage in the stack. If the system100 is configured with the battery cell 110 pulling, it may ceasepulling and may consume the PUSH command. The system 100 may determinethat the battery cell 110 is in no condition to push, even though it isidle, and may pass the PUSH command to a next cell in the stack. Theseprocesses are described hereinbelow.

A PULL command may represent a command by an external control to addnegative voltage to a load device by a stack in which the cell stage 100belongs. The stage 100 may respond to a PULL command in a variety ofways, depending on operating conditions at the stage 100. For example,if the stage 100 is configured with the battery cell 110 alreadypulling, it may continue to pull and pass the PULL command to anotherstage in the stack. If the stage 100 is configured with the battery cell110 pushing, it may cease pushing and may consume the PULL command. Thesystem 100 may determine that the battery cell 110 is in no condition topull, even though it is idle, and may pass the PULL command to a nextcell in the stack. These processes are described hereinbelow.

Although the system 100 may operate in various states (see FIGS. 2-4 andthe corresponding description of the figures below), the system may havethe following two basic configurations: (1) a “switched-in”configuration and (2) a “bypassed” or “idle” configuration. During aswitched-in configuration, the cell monitor 120 may control the switches132-138 to connect the cell 110 to the battery stack at nodes A and B.While the cell 110 is switched into the stack, the cell 110 may eitherdischarge or charge based on the needs of the stage 100 and the load. Ifswitches 132 and 138 are on and switches 134 and 134 are off, the cellmay discharge a positive voltage. If switches 134 and 136 are on andswitches 132 and 138 are off, the cell may discharge a negative voltage.

During a bypassed configuration, the cell monitor 120 may control theswitches 132-138 to disconnect the cell 110 from the battery stack atnodes A and B. While the cell 110 is bypassed from the stack, the cell110 may be prevented from being charged or discharged while theremaining stages in the stack are being charged or discharged. This mayprevent the cell 110 from being damaged by being overdischarged/charged. Based on the structure and operation of system 100above, the cell monitor 120 may balance the cell's 110 charge/dischargeoperations and prevent the cell from being damaged from over dischargingand overcharging.

The cell stage 100 optionally may include diodes 142, 144, 146, and 148coupled to the terminals of corresponding switches 132, 134, 136, and138. The diodes 142, 144, 146, and 148 may provide charge and dischargefly-back protection for the switches 132, 134, 136, and 138,respectively

FIG. 2 is a state diagram illustrating control operations of a cellstage 100 that is either charging or discharging according to anembodiment of the present invention. The state diagram illustrates aresponse of a cell monitor 120 when it receives PUSH/PULL commands fromadjacent cells in a battery stack. As illustrated in FIG. 2(A), the cellmonitor 120 may make switch-in/bypass configuration decisions inresponse to PUSH/PULL commands received via the out-bound (or upstream)or in-bound (or downstream) communication pathways 150 and 160,respectively, according to the processes outlined below. Each arrow inFIG. 2(A) is designated by a number (1)-(56) for convenience.

FIG. 2(A) illustrates an idle state 210, representing a bypassedconfiguration of the stage 100. When in the idle state, the stage 100may response to received commands in a variety of ways. For example, ifthe controller 121 of the cell monitor 120 receives a PUSH command onthe out-bound communication pathway 150 (OBCMD=“PUSH” (1)), thecontroller 121 may determine a direction of current flow through thestack. If the battery stack is either charging or discharging and thecurrent flowing through the stage 100 is flowing against the directionof the charge or discharge (5), the cell controller 121 may pass thePUSH command further up the out-bound communication pathway 150 (6) andreturn to the idle state 210 (7). If the battery stack is eithercharging or discharging and the current flowing through the stage 100 isflowing with the direction of the charge or discharge (8), the cellcontroller 121 may determine whether the cell 110 is in a condition topush (i.e., either charge or discharge). If the cell 110 cannot push(i.e., charge or discharge) (9), the cell controller 121 may pass thePUSH command further up the OBCP 150 (6) and return to the idle state210 (7). If the cell 110 can push (i.e., charge or discharge) (10), thecell controller 121 may control the switches 132-138 to switch the cell110 into the stack in a positive orientation. The stage 100 may thenenter the out-bound positive orientation (OB POS) state 220 and eithercharge or discharge the cell 110.

When in the idle state 210, if the controller 121 of the cell monitor120 receives a PULL command on the out-bound communication pathway 150(OBCMD=“PULL” (2)), the controller 121 may determine a direction ofcurrent flow through the stack. If the battery stack is either chargingor discharging and the current flowing through the stage 100 is flowingagainst the direction of the charge or discharge (11), the cellcontroller 121 may pass the PULL command further up the out-boundcommunication pathway 150 (12) and return to the idle state 210 (13). Ifthe battery stack is either charging or discharging and the currentflowing through the system 100 is flowing with the direction of thecharge or discharge (14), the cell controller 121 may determine whetherthe cell 110 is in a condition to pull (i.e. charge or discharge). Ifthe cell 110 cannot pull (i.e., charge or discharge) (15), the cellcontroller 121 may pass the PULL command further up the OBCP and returnto the idle state 210 (13). If the cell 110 can pull (i.e., charge ordischarge) (16), the cell controller 121 may control the switches132-138 to switch the cell 110 into the stack in a negative orientation.The stage 100 may then enter the out-bound negative orientation (OB NEG)state 230 and either charge or discharge the cell 110.

When in the idle state 210, if the controller 121 of the cell monitor120 receives a PUSH command on the in-bound communication pathway 160(IBCMD=“PUSH” (3)), the controller 121 may determine the condition ofthe battery cell 110. If the cell 110 cannot push (i.e., charge ordischarge) (17), the cell controller 121 may pass the PUSH commandfurther down the IBCP 160 (18) and return to the idle state 210 (19). Ifthe cell 110 can push (i.e., charge or discharge) (20), the cellcontroller 121 may control the switches 132-138 to switch the cell 110into the stack in a positive orientation and enter the in-bound positiveorientation (IB POS) state 240 to either charge or discharge the cell110.

While in the idle state 210, if the controller 121 of the cell monitor120 receives a PULL command on the in-bound communication pathway 160(IBCMD=“PULL” (4)), the controller 121 may determine the condition ofthe battery cell 110. If the cell 110 cannot pull (i.e., charge ordischarge) (21), the cell controller 121 may pass the PULL commandfurther down the IBCP (22) and return to the idle state 210 (23). If thecell 110 can pull (i.e., charge or discharge) (24), the cell controller121 may control the switches 132-138 to switch the cell 110 into thestack in a negative orientation and enter the in-bound negativeorientation (IB NEG) state 250 to either charge or discharge the cell110.

When the stage 100 is in the OB POS state 220, the stage 100 may respondto received commands in a variety of ways. For example, if thecontroller 121 receives a PUSH command on the out-bound communicationpathway 150 (i.e., OBCMD=“PUSH” (25)), the controller 121 may pass thePUSH command further up the OBCP 150 (26) and return to the OB POS 220state (27). If, the controller 121 receives a PUSH command on thein-bound communication pathway 160 (i.e., IBCMD=“PUSH” (28)), thecontroller 121 may pass the PUSH command further down the IBCP 160 (29)and return to the OB POS 220 state (30). If the controller 121 receives,on either the IBCP 160 or OBCP 150, a PULL command (32), the controller121 may revert back to the idle state 210. In the absence of a command,if the controller 121 determines that operating conditions have takenthe cell 110 outside its operating limits (e.g., either too weak todischarge or too full to charge) (31), the cell controller 121 may passa locally generated PUSH command further up the OBCP 150 (6) and revertback to the idle state 210 (7).

When the stage 100 is in the OB NEG state 230, the stage 100 may respondto received commands in a variety of ways. For example, if thecontroller 121 receives a PULL command on the out-bound communicationpathway 150 (i.e., OBCMD=“PULL” (33)), the controller 121 may pass thePULL command further up the OBCP (34) and return to the OB NEG 230 state(35). If the controller 121 receives a PULL command on the in-boundcommunication pathway 160 (i.e., IBCMD=“PULL” (36)), the controller 121may pass the PULL command further down the IBCP 160 (37) and return tothe OB NEG 230 state (38). If the controller 121 receives, on either theIBCP 160 or OBCP 150, a PUSH command (47), the controller 121 may revertback to the idle state 210. In the absence of a command, if thecontroller 121 determines that operating conditions have taken the cell110 outside its operating limits (e.g., either too weak to discharge ortoo full to charge) (56), the cell controller 121 may pass a locallygenerated PULL command further up the OBCP 150 (12) and revert back tothe idle state 210 (13).

When the stage 100 is in the IB POS state 240, the stage 100 may respondto received commands in a variety of ways. For example, if thecontroller 121 receives a PUSH command on the out-bound communicationpathway 150 (i.e., OBCMD=“PUSH” (39)), the controller 121 may pass thePUSH command further up the OBCP (40) and remain in the IB POS 240 state(41). If the controller 121 receives a PUSH command on the in-boundcommunication pathway 160 (i.e., IBCMD=“PUSH” (42)), the controller 121may pass the PUSH command further down the IBCP 160 (43) and remain inthe IB POS 240 state (44). If the controller 121 receives, on either theIBCP 160 or OBCP 150, a PULL command (46), the controller 121 may revertback to the idle state 210. In the absence of a command, if thecontroller 121 determines that operating conditions have taken the cell110 outside its operating limits (e.g., either too weak to discharge ortoo full to charge) (45), the cell controller 121 may pass a locallygenerated PUSH command further down the IBCP 160 (18) and revert back tothe idle state 210 (19).

When the stage 100 is in the IB NEG state 250, the stage 100 may respondto received commands in a variety of ways. For example, if thecontroller 121 receives a PULL command on the out-bound communicationpathway 150 (i.e., OBCMD=“PULL” (48)), the controller 121 may pass thePULL command further up the OBCP 150 (49) and return to the IB NEG 250state (50). If the controller 121 receives a PULL command on thein-bound communication pathway 160 (i.e., IBCMD=“PULL” (51)), thecontroller 121 may pass the PULL command further down the IBCP 160 (52)and remain in the IB NEG 250 state (53). If the controller 121 receives,on either the IBCP 160 or OBCP 150, a PUSH command (55), the controller121 may revert back to the idle state 210. In the absence of a command,if the controller 121 determines that operating conditions have takenthe cell 110 outside its operating limits (e.g., either too weak todischarge or too full to charge) (54), the cell controller 121 may passa locally generated PULL command further down the IBCP 160 (22) andrevert back to the idle state 210 (23).

FIG. 3 is a state diagram illustrating control operations of a cellstage 100 that is discharging according to an embodiment of the presentinvention. The state diagram illustrates a response of a cell monitor120 when it receives PUSH/PULL commands from adjacent cells in a batterystack. As illustrated in FIG. 3, the cell monitor 120 may makeswitch-in/bypass configuration decisions in response to PUSH/PULLcommands received via the out-bound (or upstream) or in-bound (ordownstream) communication pathways 150 and 160, respectively, accordingto the processes outlined below. Each arrow in FIG. 3 is designated by anumber (1)-(56) for convenience.

FIG. 3 illustrates an idle state 310, representing a bypassedconfiguration of the stage 100. When in the idle state, the stage 100may response to received commands in a variety of ways. For example, ifthe controller 121 of the cell monitor 120 receives a PUSH command onthe out-bound communication pathway 150 (OBCMD=“PUSH” (1)), thecontroller 121 may determine a direction of current flow through thestack. If the battery stack is discharging and the current flowingthrough the stage 100 is incoming (5), the cell controller 121 may passthe PUSH command further up the out-bound communication pathway 150 (6)and return to the idle state 310 (7). If the battery stack isdischarging and the current flowing through the stage 100 is notincoming (8), the cell controller 121 may determine whether the cell 110is in a condition to push (i.e., discharge). If the cell 110 cannot push(i.e., discharge) (9), the cell controller 121 may pass the PUSH commandfurther up the OBCP 150 (6) and return to the idle state 310 (7). If thecell 110 can push (i.e., discharge) (10), the cell controller 121 maycontrol the switches 132-138 to switch the cell 110 into the stack in apositive orientation. The stage 100 may then enter the out-boundpositive orientation (OB POS) state 320 and discharge the cell 110.

When in the idle state 310, if the controller 121 of the cell monitor120 receives a PULL command on the out-bound communication pathway 150(OBCMD=“PULL” (2)), the controller 121 may determine a direction ofcurrent flow through the stack. If the battery stack is discharging andthe current flowing through the stage 100 is outgoing (11), the cellcontroller 121 may pass the PULL command further up the out-boundcommunication pathway 150 (12) and return to the idle state 310 (13). Ifthe battery stack is discharging and the current flowing through thesystem 100 is not outgoing (14), the cell controller 121 may determinewhether the cell 110 is in a condition to pull (i.e. discharge). If thecell 110 cannot pull (i.e., discharge) (15), the cell controller 121 maypass the PULL command further up the OBCP and return to the idle state310 (13). If the cell 110 can pull (i.e., discharge) (16), the cellcontroller 121 may control the switches 132-138 to switch the cell 110into the stack in a positive orientation. The stage 100 may then enterthe out-bound negative orientation (OB NEG) state 330 and discharge thecell 110.

When in the idle state 310, if the controller 121 of the cell monitor120 receives a PUSH command on the in-bound communication pathway 160(IBCMD=“PUSH” (3)), the controller 121 may determine the condition ofthe battery cell 110. If the cell 110 cannot push (i.e., discharge)(17), the cell controller 121 may pass the PUSH command further down theIBCP 160 (18) and return to the idle state 310 (19). If the cell 110 canpush (i.e., discharge) (20), the cell controller 121 may control theswitches 132-138 to switch the cell 110 into the stack in a positiveorientation and enter the in-bound positive orientation (IB POS) state340 to discharge the cell 110.

While in the idle state 310, if the controller 121 of the cell monitor120 receives a PULL command on the in-bound communication pathway 160(IBCMD=“PULL” (4)), the controller 121 may determine the condition ofthe battery cell 110. If the cell 110 cannot pull (i.e., discharge)(21), the cell controller 121 may pass the PULL command further down theIBCP 160 (22) and return to the idle state 310 (23). If the cell 110 canpull (i.e., discharge) (24), the cell controller 121 may control theswitches 132-138 to switch the cell 110 into the stack in a negativeorientation and enter the in-bound negative orientation (IB NEG) state350 to discharge the cell 110.

When the stage 100 is in the OB POS state 320, the stage 100 may respondto received commands in a variety of ways. For example, if thecontroller 121 receives a PUSH command on the out-bound communicationpathway 150 (i.e., OBCMD=“PUSH” (25)), the controller 121 may pass thePUSH command further up the OBCP 150 (26) and return to the OB POS 320state (27). If, the controller 121 receives a PUSH command on thein-bound communication pathway 160 (i.e., IBCMD=“PUSH” (28)), thecontroller 121 may pass the PUSH command further down the IBCP 160 (29)and return to the OB POS 320 state (30). If the controller 121 receives,on either the IBCP 160 or OBCP 150, a PULL command (32), the controller121 may revert back to the idle state 310. In the absence of a command,if the controller 121 determines that the cell 110 is weakening (i.e.,weakening below a predetermined limit so it can no longer discharge)(31), the cell controller 121 may pass a locally generated PUSH commandfurther up the OBCP 150 (6) and revert back to the idle state 310 (7).

When the stage 100 is in the OB NEG state 330, the stage 100 may respondto received commands in a variety of ways. For example, if thecontroller 121 receives a PULL command on the out-bound communicationpathway 150 (i.e., OBCMD=“PULL” (33)), the controller 121 may pass thePULL command further up the OBCP 150 (34) and return to the OB NEG 330state (35). If the controller 121 receives a PULL command on thein-bound communication pathway 160 (i.e., IBCMD=“PULL” (36)), thecontroller 121 may pass the PULL command further down the IBCP 160 (37)and return to the OB NEG 330 state (38). If the controller 121 receives,on either the IBCP 160 or OBCP 150, a PUSH command (47), the controller121 may revert back to the idle state 310. In the absence of a command,if the controller 121 determines that the cell 110 is weakening (i.e.,weakening below a predetermined limit so it can no longer discharge)(56), the cell controller 121 may pass a locally generated PULL commandfurther up the OBCP 150 (12) and revert back to the idle state 310 (13).

When the stage 100 is in the IB POS state 340, the stage 100 may respondto received commands in a variety of ways. For example, if thecontroller 121 receives a PUSH command on the out-bound communicationpathway 150 (i.e., OBCMD=“PUSH” (39)), the controller 121 may pass thePUSH command further up the OBCP 150 (40) and remain in the IB POS 340state (41). If the controller 121 receives a PUSH command on thein-bound communication pathway 160 (i.e., IBCMD=“PUSH” (42)), thecontroller 121 may pass the PUSH command further down the IBCP 160 (43)and remain in the IB POS 340 state (44). If the controller 121 receives,on either the IBCP 160 or OBCP 150, a PULL command (46), the controller121 may revert back to the idle state 310. In the absence of a commandif the controller 121 determines that the cell 110 is weakening (i.e.,weakening below a predetermined limit so it can no longer discharge)(45), the cell controller 121 may pass a locally generated PUSH commandfurther down the IBCP 160 (18) and revert back to the idle state 310(19).

When the stage 100 is in the IB NEG state 350, the stage 100 may respondto received commands in a variety of ways. For example, if thecontroller 121 receives a PULL command on the out-bound communicationpathway 150 (i.e., OBCMD=“PULL” (48)), the controller 121 may pass thePULL command further up the OBCP 150 (49) and return to the IB NEG 350state (50). If the controller 121 receives a PULL command on thein-bound communication pathway 160 (i.e., IBCMD=“PULL” (51)), thecontroller 121 may pass the PULL command further down the IBCP 160 (52)and remain in the IB NEG 350 state (53). If the controller 121 receives,on either the IBCP 160 or OBCP 150, a PUSH command (55), the controller121 may revert back to the idle state 310. In the absence of a command,if the controller 121 determines that the cell 110 is weakening (i.e.,weakening below a predetermined limit so it can no longer discharge)(54), the cell controller 121 may pass a locally generated PULL commandfurther down the IBCP 160 (22) and revert back to the idle state 310(23).

FIG. 4 is a state diagram illustrating control operations of a cellstage 100 that is charging according to an embodiment of the presentinvention. The state diagram illustrates a response of a cell monitor120 when it receives PUSH/PULL commands from adjacent cells in a batterystack. As illustrated in FIG. 4, the cell monitor 120 may makeswitch-in/bypass configuration decisions in response to PUSH/PULLcommands received via the out-bound (or upstream) or in-bound (ordownstream) communication pathways 150 and 160, respectively, accordingto the processes outlined below. Each arrow in FIG. 4 is designated by anumber (1)-(56) for convenience.

FIG. 4 illustrates an idle state 410, representing a bypassedconfiguration of the stage 100. When in the idle state, the stage 100may response to received commands in a variety of ways. For example, ifthe controller 121 of the cell monitor 120 receives a PUSH command onthe out-bound communication pathway 150 (OBCMD=“PUSH” (1)), thecontroller 121 may determine a direction of current flow through thestack. If the battery stack is charging and the current flowing throughthe stage 100 is outgoing (5), the cell controller 121 may pass the PUSHcommand further up the out-bound communication pathway 150 (6) andreturn to the idle state 410 (7). If the battery stack is charging andthe current flowing through the stage 100 is not outgoing (8), the cellcontroller 121 may determine whether the cell 110 is in a condition topush (i.e., charge). If the cell 110 cannot push (i.e., charge) (9), thecell controller 121 may pass the PUSH command further up the OBCP 150(6) and return to the idle state 410 (7). If the cell 110 can push(i.e., charge) (10), the cell controller 121 may control the switches132-138 to switch the cell 110 into the stack in a positive orientation.The stage 100 may then enter the out-bound positive orientation (OB POS)state 420 and charge the cell 110.

When in the idle state 410, if the controller 121 of the cell monitor120 receives a PULL command on the out-bound communication pathway 150(OBCMD=“PULL” (2)), the controller 121 may determine a direction ofcurrent flow through the stack. If the battery stack is charging and thecurrent flowing through the stage 100 is incoming (11), the cellcontroller 121 may pass the PULL command further up the out-boundcommunication pathway 150 (12) and return to the idle state 410 (13). Ifthe battery stack is charging and the current flowing through the system100 is not incoming (14), the cell controller 121 may determine whetherthe cell 110 is in a condition to pull (i.e. charge). If the cell 110cannot pull (i.e., charge) (15), the cell controller 121 may pass thePULL command further up the OBCP 150 and return to the idle state 410(13). If the cell 110 can pull (i.e., charge) (16), the cell controller121 may control the switches 132-138 to switch the cell 110 into thestack in a positive orientation. The stage 100 may then enter theout-bound negative orientation (OB NEG) state 430 and charge the cell110.

When in the idle state 410, if the controller 121 of the cell monitor120 receives a PUSH command on the in-bound communication pathway 160(IBCMD=“PUSH” (3)), the controller 121 may determine the condition ofthe battery cell 110. If the cell 110 cannot push (i.e., charge ordischarge) (17), the cell controller 121 may pass the PUSH commandfurther down the IBCP 160 (18) and return to the idle state 410 (19). Ifthe cell 110 can push (i.e., charge or discharge) (20), the cellcontroller 121 may control the switches 132-138 to switch the cell 110into the stack in a positive orientation and enter the in-bound positiveorientation (IB POS) state 440 to charge the cell 110.

While in the idle state 410, if the controller 121 of the cell monitor120 receives a PULL command on the in-bound communication pathway 160(IBCMD=“PULL” (4)), the controller 121 may determine the condition ofthe battery cell 110. If the cell 110 cannot pull (i.e., charge ordischarge) (21), the cell controller 121 may pass the PULL commandfurther down the IBCP 160 (22) and return to the idle state 410 (23). Ifthe cell 110 can pull (i.e., charge or discharge) (24), the cellcontroller 121 may control the switches 132-138 to switch the cell 110into the stack in a negative orientation and enter the in-bound negativeorientation (IB NEG) state 450 to charge the cell 110.

When the stage 100 is in the OB POS state 420, the stage 100 may respondto received commands in a variety of ways. For example, if thecontroller 121 receives a PUSH command on the out-bound communicationpathway 150 (i.e., OBCMD=“PUSH” (25)), the controller 121 may pass thePUSH command further up the OBCP 150 (26) and return to the OB POS 420state (27). If, the controller 121 receives a PUSH command on thein-bound communication pathway 160 (i.e., IBCMD=“PUSH” (28)), thecontroller 121 may pass the PUSH command further down the IBCP 160 (29)and return to the OB POS 420 state (30). If the controller 121 receives,on either the IBCP 160 or OBCP 150, a PULL command (32), the controller121 may revert back to the idle state 410. In the absence of a command,if the controller 121 determines that the cell 110 is filling (i.e., thecell 110 should not be charged above a predetermined limit to preventdamage to the cell 110) (31), the cell controller 121 may pass a locallygenerated PUSH command further up the OBCP 150 (6) and revert back tothe idle state 410 (7).

When the stage 100 is in the OB NEG state 430, the stage 100 may respondto received commands in a variety of ways. For example, if thecontroller 121 receives a PULL command on the out-bound communicationpathway 150 (i.e., OBCMD=“PULL” (33)), the controller 121 may pass thePULL command further up the OBCP 150 (34) and return to the OB NEG 430state (35). If the controller 121 receives a PULL command on thein-bound communication pathway 160 (i.e., IBCMD=“PULL” (36)), thecontroller 121 may pass the PULL command further down the IBCP 160 (37)and return to the OB NEG 430 state (38). If the controller 121 receives,on either the IBCP 160 or OBCP 150, a PUSH command (47), the controller121 may revert back to the idle state 410. In the absence of a command,if the controller 121 determines that the cell 110 is filling (i.e., thecell 110 should not be charged above a predetermined limit to preventdamage to the cell 110) (56), the cell controller 121 may pass a locallygenerated PULL command further up the OBCP 150 (12) and revert back tothe idle state 410 (13).

When the stage 100 is in the IB POS state 440, the stage 100 may respondto received commands in a variety of ways. For example, if thecontroller 121 receives a PUSH command on the out-bound communicationpathway 150 (i.e., OBCMD=“PUSH” (39)), the controller 121 may pass thePUSH command further up the OBCP 150 (40) and remain in the IB POS 440state (41). If the controller 121 receives a PUSH command on thein-bound communication pathway 160 (i.e., IBCMD=“PUSH” (42)), thecontroller 121 may pass the PUSH command further down the IBCP 160 (43)and remain in the IB POS 440 state (44). If the controller 121 receives,on either the IBCP 160 or OBCP 150, a PULL command (46), the controller121 may revert back to the idle state 410. In the absence of a commandif the controller 121 determines that the cell 110 is filling (i.e., thecell 110 should not be charged above a predetermined limit to preventdamage to the cell 110) (45), the cell controller 121 may pass a locallygenerated PUSH command further down the IBCP 160 (18) and revert back tothe idle state 410 (19).

When the stage 100 is in the IB NEG state 450, the stage 100 may respondto received commands in a variety of ways. For example, if thecontroller 121 receives a PULL command on the out-bound communicationpathway 150 (i.e., OBCMD=“PULL” (48)), the controller 121 may pass thePULL command further up the OBCP 150 (49) and return to the IB NEG 450state (50). If the controller 121 receives a PULL command on thein-bound communication pathway 160 (i.e., IBCMD=“PULL” (51)), thecontroller 121 may pass the PULL command further down the IBCP 160 (52)and remain in the IB NEG 450 state (53). If the controller 121 receives,on either the IBCP 160 or OBCP 150, a PUSH command (55), the controller121 may revert back to the idle state 410. In the absence of a command,if the controller 121 determines that the cell 110 is filling (i.e., thecell 110 should not be charged above a predetermined limit to preventdamage to the cell 110) (54), the cell controller 121 may pass a locallygenerated PULL command further down the IBCP 160 (22) and revert back tothe idle state 410 (23).

FIG. 5 illustrates a battery stack 500 according to an embodiment of thepresent disclosure. The battery stack 500 may include multiple stages1-N and a stack controller 530. The stages 1-N may be similar to thestage 100 described above with respect to FIG. 1. The stack controller530 may control the operation of the stages 1-N of the battery stack 500via a communication network including outbound and inbound communicationpaths 540 and 550, respectively (described in further detail below).

Adjacent stages may be coupled to each other as described hereinbelow,forming the battery stack 500. Each stage 1-N may include terminals RX1,RX2, TX1, TX2 (shown in more detail in FIG. 1). The terminals TX1 andTX2 for each stage may be coupled to the terminals RX1 and RX2 of anadjacent stage on both the outbound path 540 and inbound path 550. Takestage 2 for example. The terminal RX1.2 of stage 2 may be coupled to theterminal TX1.1 of stage 1 via the outbound path 540. The terminal TX1.2of stage 2 may be coupled to the terminal RX1.3 of stage 3 via theoutbound path 540. The terminal RX2.2 of stage 2 may be coupled to theterminal TX3.1 of stage 3 via the inbound path 550. The terminal TX2.2may be coupled to the terminal RX2.1 of stage 1 via the inbound path550. The terminals RX1, RX2, TX1, TX2 of the remaining stages 1 and 3-Nmay be coupled to adjacent stages in a similar fashion. Moreover, theterminals RX1.1 and TX2.1 of stage 1 may be coupled to the stackcontroller 530 via the outbound and inbound paths 540 and 550.

Each stage 1-N may also include output terminals (or nodes) A and B(similar to nodes A and B of FIG. 1 described above). The output nodes Aand B for each stage 1-N may be coupled to adjacent stages in thebattery stack in a daisy chain configuration, as shown in FIG. 5. Takestage 2 for example. The output terminal A-2 of stage 2 may be coupledto the output terminal B-3 of stage 3 and the output terminal B-2 ofstage 2 may be coupled to the output terminal A-1 of stage 1. Moreover,the output terminal B-1 of stage 1 (or the bottom stage) and the outputterminal A-N of stage N (or the top stage) may be coupled to a load(e.g., a motor).

Each stage 1-N may be substantially similar to the cell controllersystem 100 of FIG. 1 in structure and operation. Each stage may includea battery cell 510.1-510.N and cell monitor (MTR) 520.1-520.N pair andswitches (562.1-568.1 for stage 1, 562.2-568.2 for stage 2, 562.3-568.3. . . and 562.N-568.N for stage N). The battery cells 510.1-510.N andthe cell MTRs 520.1-520.N are substantially similar, in structure andoperation, to the battery cell 110 and cell monitor 120, respectively,of FIG. 1. Cell monitors of adjacent cells may communicate with eachother using the terminals TX1, TX2, RX1, RX2 via the outbound andinbound communication pathways 540 and 550, respectively. Additionally,the four switches for each stage may be substantially similar, instructure and operation, to the switches 132, 134, 136, and 138 of FIG.1.

The stack controller 530 may be coupled to the cell controller 520.1 ofstage 1. The stack controller 530 may send PUSH or PULL commands to cellMRT 520.1 of stage 1 on the outbound communication pathway 540 based onthe requirements of the load (described in further detail below). Thestack controller 530 may receive a clock (CLK) signal and send timedPUSH/PULL commands up the battery stack 500. The stack controller 530may also receive communications from the cell MRT 520.1 on the inboundcommunication pathway 550 (i.e., PUSH/PULL commands that make it back tothe stack controller 530).

During operation, the stack controller 530 may control the stack 500 byswitching-in or bypassing certain cells 510.1-510.N to supply a desiredvoltage waveform to the load by sending a calculated number of PUSH/PULLcommands (based on the desired voltage waveform) to the cell MTR 520.1of stage 1 via the outbound communication pathway 540. Morespecifically, the stack controller 530 may control the stack 500 togenerate the desired voltage waveform by determining the voltagerequired by the load and using the CLK signal to send a series of timedPUSH/PULL commands to the stack 500. The cell MTR 520.1 of stage 1 maydecide whether it should be in a “switched-in” or “bypassed” state, asdescribed above with respect to FIGS. 1-4.

In other words, stage 1 would either switch-in the cell 510.1 (i.e.,comply with the PUSH/PULL command) or bypass the cell 510.1 and transmitthe PUSH/PULL command to the next cell MTR 520.2 (of the next stage 2)in the battery stack 500 via the outbound communication pathway 540. Asdescribed with respect to state diagrams of FIG. 2-4 above, theremaining cell MTRs 520.2-520.N of each corresponding stage 2-N may makeits own decision on whether to switch-in or bypass (and transmit thecommand up pathway 540) the corresponding cells 510.2-510.N until thereare no more PUSH/PULL commands in the pathway 540 (indicating that thedesired voltage waveform is being supplied). In some circumstances, thePUSH/PULL commands may be rejected by each stage 1-N in the stack andthe commands may return back down to each stage N−1 on the returncommunication pathway 550 for reconsideration.

For example, say that the battery stack 500 includes fifty cells510.1-510.50 and each cell 510.1-510.50 may be capable of supplying 4 V(when healthy). If the motor (or the load) requires +100 V during agiven acceleration operation, the stack controller 530 may transmittwenty-five sequential PUSH commands to the cell controller 520.1 ofstage 1 via the outbound communication pathway 540. The commands maypropagate up the path 540 until twenty-five cells decide to “switch-in”to supply approximately 100 V to the load. The stack controller 530 maysimilarly transmit twenty-five sequential PULL commands to control thebattery stack 500 to provide −100V to the motor.

According one embodiment, the stack controller 530 may control thebattery stack 500 to supply a constant voltage waveform (e.g., to poweran electric motor) by transmitting a series of PUSH (or PULL) commandsup the outbound communication pathway 540. The stack 500 may eventuallysupply a desired constant waveform (either positive or negative) afteran adequate number of cells are switched-in. The stack controller 530may increase the constant voltage supplied by the stack 500 by sendingmore PUSH (or PULL if a negative voltage is required) commands up theupstream communication pathway 540. Similarly, the stack controller 530may decrease the constant voltage supplied by the stack 500 duringoperation by sending a series of PULL (or PUSH) commands up the outboundcommunication pathway 540.

According to another embodiment, the stack controller 530 may controlthe battery stack 500 to supply a sinusoidal voltage waveform. In suchan embodiment, the stack controller 530 may send a plurality ofalternating sets of PUSH/PULL commands in the following repeatingsequence so the output voltage waveform may oscillate: (1) a series PUSHcommands (to switch-in cells to provide a positive voltage), (2) aseries of PULL commands (to bypass the cells that were switched-in toprovide a positive voltage in (1)), (3) a series of PULL commands (toswitch-in cells to provide a negative voltage), and (4) a series of PUSHcommands (to bypass the cells that were switched-in to provide anegative voltage in (3)). The stack controller 530 may also control thestack 500 to supply various other output waveforms as desired by theload the stack 500 is driving.

The battery stack 500 may also include diodes 572.1-578.1 (for stage 1),572.2-578.2 (for stage 2), 572.3-578.3 . . . and 572.N-578.N (for stageN), which may be optionally coupled to the switches in each stage 1-N.The diodes may provide charge and discharge fly-back protection forcorresponding battery cells 510.1-510.N in each stage 1-N, respectively.

FIG. 6 illustrates a battery stack 600 according to an alternateembodiment of the present invention. Battery stack 600 may include astack controller 630 and a plurality of stages 1-N which may be similarin structure and operation to the stack controller 530 and stages 1-N ofFIG. 5. However, the battery stack 600 of FIG. 6 may also include anisolator 680. The isolator may be any device suitable to maintain anelectric isolation between the stack controller 630 and the stage N, forexample a transformer, an optical isolator, a capacitive isolator, orthe like.

The isolator 680 may be coupled between the stack controller 630 and thelast stage N in the battery stack 600. The transformer 680 may allow thestack controller 630 to directly communicate with the stage N cell MTR620.N without damaging the stack controller 630. The stack controller630 may not otherwise be able to directly communicate with the laststage N because doing so would expose the stack controller 630 to thehigh voltages present on stage N of the stack 600 (the high voltages maydamage the stack controller 630).

The battery stack 600 may optionally include another transformer 690coupled between the last stage N and the stack controller 630. Thetransformer 690 may allow the stack controller 630 to directlycommunicate with the stage N cell MRT 620.N without damaging the stackcontroller 630. The stack controller 630 may not otherwise be able todirectly receive communicate with the last stage N because doing sowould expose the stack controller 630 to the high voltages present onstage N of the stack 600 (the high voltages may damage the stackcontroller 630).

FIG. 7 illustrates a battery pack 700 including a battery cell 710 withan integrated controller 720 for fault protection. The battery pack 700may include a battery cell 710, a local controller 720, MOSFETtransistors 732, 734, 736, and 738, output terminals T1 and T2, andpower terminals “P.” The gate terminals of the transistors 732-738 maybe coupled to the controller 720 in an H-Bridge configuration, asillustrated in FIG. 7. The drain terminals of the transistors 732 and734 may be coupled a positive terminal (“+”) of the battery cell 710 andthe source terminals of transistors 732 and 734 may be coupled to theoutput terminals T1 and T2, respectively. The source terminals of thetransistors 736 and 738 may be coupled a negative terminal (“−”) of thebattery cell 710 and the drain terminals of transistors 736 and 738 maybe coupled to the output terminals T1 and T2, respectively. Thecontroller 720 may also be coupled the + and − terminals of the cell 710and the power terminals P.

The cell 710 may be a lead-acid, nickel-metal hydride (NiMH),lithium-ion (Li-ion), or other type of battery that may be integrated ina battery stack to provide power to drive hybrid vehicles. The cell 710may include a positive terminal “+” and a negative terminal “−” whichmay be selectively coupled to terminals T1 and T2. The terminals T1 andT2 may be coupled to terminals of adjacent battery packs in a stack ofbatteries used to drive a load (similar to the battery stack of FIG. 5).

The controller 720 (which may be similar to controller 121 of FIG. 1 orcontroller 520 in FIG. 5) may include a microcontroller, a programmableprocessor, and/or a state machine and may measure the condition of thecell 710 (via terminals + and −) as well as the current flowing betweenT1 to T2 to determine the presence of a fault. The controller 720 may becoupled to power terminals P, which may provide a communication channelallowing the controller 720 to communicate (send PUSH/PULL) command toadjacent cells in the battery stack (in a similar manner as describedabove with respect to FIGS. 1-6). The controller 720 may be internallypowered by the cell 710.

Transistors 732-738 may be MOSFETS of sufficient size to serve as powertransistors or mechanical switches. Transistors 732 and 738 may bedepletion mode MOSFETs (i.e., current flows through them when they areoff) and transistors 734 and 736 may be enhancement mode MOSFETs (i.e.,current flows through them when they are on).

During regular operation (i.e., the controller 720 is not activating theswitches 732-738), the “+” terminal of cell 710 may be coupled to T1 andthe “−” terminal of cell 710 may be coupled to T2. Thus, even if thecontroller malfunctions or breaks, the battery cell 710 may still becoupled to terminals T1 and T2, so the cell 710 is not bypassed in thebattery stack.

If the controller 720 determines that there is a large current flowingbetween T1 to T2 (i.e., a fault condition), the controller 720 maydetermine that the cell 710 may be in danger of being damaged. In suchcases, the controller 720 may switch depletion mode MOSFETs 732 and 738on so they are not conducting current and leave enhancement mode MOSFETs734 and 736 off so they are not conducting current. This operationeffectively isolates the battery cell 710 from the high current flowingbetween the terminals T1 and T2 so that the cell 710 remains undamaged.This type of “fault protection” may be useful when the cells of abattery stack are subject to catastrophic events such as submersion.Moreover, the battery pack 700 may be a water-tight enclosure to preventwater from entering into the package and damaging the cell 710 and thecontroller 720. The controller 720 may also monitor (using a sensorsimilar to the sensor shown in FIG. 1) the temperature inside thebattery pack 700. If the temperature is too high (above a predefinedlimit), this may also indicate a fault condition, and the controller 720may disconnect the battery cell 710 from the terminals T1 and T2 asdescribed above.

The battery pack 700 may be integrated in a battery stack similar to thebattery stacks described in FIGS. 5 and 6 above. In such systems, eachbattery cell and controller pair (or “stage”) may be provided in acommon battery package 700 as shown in FIG. 7. Each stage may operate ina similar fashion to the stages described above in FIGS. 1-5 and maycommunicate with neighboring stages over a communication network (asshown in FIGS. 4 and 5) as described above.

The battery pack 700 may also include diodes 742, 744, 746, and 748,which may be coupled to a source and drain terminal of correspondingtransistors 732, 734, 736, and 738. The diodes 742, 744, 746, and 748may be optionally included to provide charge and discharge fly-backprotection for the transistors 732, 734, 736, and 738.

FIG. 8 is a simplified block diagram of a cell controller communicationnetwork 800 implementing a leapfrogging protocol according to anembodiment of the present disclosure. The diagram in FIG. 8 omits thebattery cells and switches in FIGS. 1, 5, and 6, for simplificationpurposes, and focuses on a communication network 800 between the cellcontrollers in a plurality of stages of a battery stack. Thecommunication network 800 may include a plurality of cell monitors810.1-810.N which may be connected in a “leapfrogging” configuration860. In a leapfrogging configuration, each cell monitor 810.1, 810.2,810.3 . . . 810.N may be coupled to the closest two neighboring cellmonitors succeeding it in the network 800 and the closest twoneighboring cell monitors preceding it in the network 800.

Each cell monitor, say monitor 810.1, may include a local controller820.1, a local transmitter 830.1, a first local receiver 840.1, and asecond local receiver 850.1. Each local controller 820.1 may be coupledto a respective local transmitter 830.1, a first local receiver 840.1,and a second local receiver 850.1. Each first local receiver 840.1 maybe coupled to a transmitter of an immediately preceding cell controllerin the network 800. Each second local receiver 850.1 may “leapfrog” theimmediately preceding cell monitor and may be coupled to a transmitterof a cell controller that is two nodes down the network 800.

Take cell monitor 810.3 for example. The first local receiver 840.3 maybe coupled to the transmitter 830.2 in cell monitor 810.2. The secondlocal receiver 850.3 may be coupled to the transmitter 830.1 in cellmonitor 810.1.

The operation of each cell monitor 810.1-810.N in the communicationnetwork 800 will now be described using cell monitor 810.3 as anexample. During normal operation, the first local receiver 840.3 mayreceive PUSH/PULL commands from the transmitter 830.2 in cell monitor810.2. The controller 820.3 may process the received PUSH/PULL commandand determine whether to PUSH/PULL a corresponding battery cell ortransmit, using the local transmitter 830.3, the received PUSH/PULLcommand to the next cell monitor 810.4 in the network 800 (this processis described in more detail above with respect to FIGS. 1-6).

In some cases, however, there may be a fault in the communicationnetwork 800. The cell controller 820.3 of cell monitor 810.3 may“eavesdrop” on the transmitter 830.1 of the cell monitor 810.1. If cellmonitor 810.1 transmits, via transmitter 830.1, two commands (eitherPUSH or PULL) to cell monitor 810.2 and the transmitter 830.2 neverpasses a command (either PUSH or PULL) to cell monitor 810.3, the cellcontroller 820.3 of cell monitor 810.3 may determine that there is afault in cell monitor 810.2. If there is a fault detected in thismanner, the controller 820.3 may “leapfrog” (or bypass) the cell monitor810.2 in the network 800 and respond to PUSH/PULL commands from the cellmonitor 810.1 henceforth.

Each cell monitor 810.1-810.N in the network 800 may follow theleapfrogging protocol described above to prevent a fault in any one ofthe cell monitor 810.1, 810.2, 810.3 . . . -810.N from disabling theentire communication network 800.

According to another embodiment of the present invention, the controller820.3 of cell monitor 810.3 may determine that it has not received aPUSH/PULL command from the preceding cell controller 810.2 in thenetwork 800 for a predetermined period of time. The absence of PUSH/PULLcommands received from the preceding cell monitor 810.2 may indicatethat cell controller 810.2 is faulty. In such cases, the cell controller820.3 may determine whether the second local receiver 850.3 has receiveda PUSH/PULL command from the transmitter 830.1 in the cell monitor 810.1that is two nodes down the communication network 800 during the sameperiod of time.

If the transmitter 830.1 in the cell monitor 810.1 has not transmittedany PUSH/PULL command during the same period of time, the controller820.3 may determine that there is nothing wrong with cell monitor 810.2and that there are simply no PUSH/PULL commands in the network 800. If,however, the transmitter 830.1 has transmitted PUSH/PULL commands duringthe same period of time, the controller 820.3 may determine that cellmonitor 810.2 is faulty. If cell the monitor 810.2 is faulty, thecontroller 820.3 may “leapfrog” (or bypass) the cell monitor 810.2 inthe network 800 and respond to PUSH/PULL commands from the cell monitor810.1 henceforth.

Although the foregoing techniques have been described above withreference to specific embodiments, the invention is not limited to theabove embodiments and the specific configurations shown in the drawings.For example, some components shown may be combined with each other asone embodiment, or a component may be divided into severalsubcomponents, or any other known or available component may be added.Those skilled in the art will appreciate that these techniques may beimplemented in other ways without departing from the spirit andsubstantive features of the invention. The present embodiments aretherefore to be considered in all respects as illustrative and notrestrictive.

We claim:
 1. A system comprising: a first local controller to control a,first switch system to selectively connect and disconnect a firstbattery cell of a first stage of a battery stack; and a second localcontroller to control a, second switch system to selectively connect anddisconnect a second battery cell of a second stage of the battery stack,wherein the second local controller and the first local controller arein communication by a daisy chain communication system; and a stackcontroller connected to the communication system to send command signalsto the first local controller and the second local controllerrepresenting desired changes in an output voltage of the battery stack,wherein the first local controller receives a first command from thestack controller and determines, based at least in part on localoperating conditions of the first battery cell, to pass the firstcommand to the second local controller, and wherein the second localcontroller receives the first command from the first local controllerand determines, based at least in part on local operating conditions ofthe second battery cell, to consume the first command.
 2. The system ofclaim 1, wherein the first local controller is in communication with afirst receiver to receive the command signals; and a first sensor tomeasure operating conditions of the first battery cell.
 3. The system ofclaim 2, wherein the first sensor is to measure a direction of currentflowing through the first battery cell and the local operatingconditions of the first battery cell comprise the direction of currentflowing through the first battery cell.
 4. The system of claim 2,wherein the first sensor is to measure a state of charge of the firstbattery cell and the local operating conditions of the first batterycell comprise the state of charge of the first battery cell.
 5. Thesystem of claim 1, wherein the first local controller is incommunication with memory to store the local operating conditions of thefirst battery cell.
 6. The system of claim 1, wherein the first localcontroller is in communication with a memory to store a configuration ofthe first switch system.
 7. The system of claim 1, wherein thecommunication system is bidirectional.
 8. The system of claim 1, whereinthe communication system is unidirectional.
 9. The system of claim 1,wherein the output voltage is a unipolar.
 10. The system of claim 1,wherein the output voltage is a hi-polar waveform.
 11. The system ofclaim 1, further comprising an isolator provided in the communicationsystem coupled between a last stage of the battery stack and the stackcontroller.
 12. The system of claim 1, wherein the first switch systemcomprises a plurality of field-effect transistors (FETs).
 13. The systemof claim 12, wherein the plurality of FETs are coupled to the batterycell in an H-bridge configuration.
 14. The system of claim 1, furthercomprising the battery stack, wherein the battery stack comprises: thefirst stage, wherein the first stage comprises the first battery cell;and the second stage, wherein the second stage comprises the secondbattery cell.
 15. A method comprising: transmitting a plurality ofcommand signals over a communication network, using a battery stackcontroller, to a battery stack comprising a plurality of battery stages,wherein each stage comprises: an associated battery cell, a localcontroller, and a switch system, wherein the command signals representdesired changes in an output voltage of the stack; and for each stage,the local controller controlling the switch system to selectivelyconnect or disconnect the associated battery cell from the batterystack; receiving, by a first local controller of a first battery stageof the plurality of battery stages, a first command from the batterystack controller; determining, by the first local controller, to passthe first command to a second local controller of a second battery stageof the plurality of battery stages based at least in part on localoperating conditions at the first battery stage; receiving, by thesecond local controller, the first command from the first localcontroller; and determining, by the second local controller, to consumethe first command based at least in part on local operating conditionsat the second battery stage.
 16. The method of claim 15, wherein eachstage further comprises: a receiver to receive the command signals; anda sensor to measure the local operating conditions of the associatedbattery cell.
 17. The method of claim 14, further comprising measuring adirection of current flowing through a first battery cell of the firstbattery stage and controlling a first switch system of the first batterystage based on the direction of current flowing through the firstbattery cell.
 18. The method of claim 15, further comprising measuring astate of charge of a first battery cell of the first stage.
 19. Themethod of claim 15, wherein the first local controller is incommunication with a memory to store the local operating conditions of afirst battery cell and a configuration of the switch system.
 20. Themethod of claim 15, wherein the first local controller is incommunication with a memory to store a configuration of a first switchsystem.
 21. The method of claim 15, wherein the communication network isbidirectional.
 22. The method of claim 15, wherein the communicationnetwork is unidirectional.
 23. The method of claim 15, wherein theoutput voltage is a unipolar voltage.
 24. The method of claim 15,wherein the output voltage is a bi-polar voltage waveform.
 25. Themethod of claim 15, further comprising providing an isolator in thecommunication network between a last stage of the battery stack and thestack controller.
 26. The method of claim 15, wherein a first switchsystem of the first battery stage comprises a plurality of field effecttransistors (FETs).
 27. The method of claim 26, wherein the plurality ofFETs are coupled to the associated battery cell in an H-bridgeconfiguration.
 28. A system comprising: a first local controller tocontrol a first switch system to selectively connect and disconnect afirst battery cell of a first stage of a plurality of stages of abattery stack; and a second local controller to control a second switchsystem to selectively connect and disconnect a second battery cell of asecond stage of the plurality of stages of the battery stack, whereinthe second local controller and the first local controller are incommunication by a daisy chain communication system; a stack controllerconnected to the communication system to send command signals to thestack representing desired changes in an output voltage of the stack;and an isolator coupled between a last stage of the plurality of stagesof the battery stack and the stack controller, wherein the first localcontroller receives a first command from the stack controller anddetermines, based at least in part on local operating conditions of thefirst battery cell, to pass the first command to the second localcontroller, and wherein the second local controller receives the firstcommand from the first local controller and determines, based at leastin part on local operating conditions of the second battery cell, toconsume the first command.
 29. The system of claim 28, wherein the firstlocal controller further comprises a first receiver to receive thecommand signals.
 30. The system of claim 29, wherein the first localcontroller is in communication with a first sensor that measures adirection of current flowing through the first battery cell, and wherethe local operating conditions of the first battery cell comprise thedirection of current flowing through the first battery cell.
 31. Thesystem of claim 29, wherein the first local controller is incommunication with a first sensor that measures a state of charge of thefirst battery cell, and wherein the local operating conditions of thefirst battery cell comprise the state of charge of the battery cell. 32.The system of claim 28, wherein the first local controller is incommunication with a memory to store operating conditions of the firstbattery cell.
 33. The system of claim 28, wherein the first localcontroller is in communication with a memory to store a configuration ofthe first switch system.
 34. The system of claim 28, wherein thecommunication system is unidirectional.
 35. The system of claim 28,wherein the output voltage is a unipolar voltage.
 36. The system ofclaim 28, wherein the output voltage is a bi-polar waveform.
 37. Thesystem of claim 28, wherein the first switch system comprises aplurality of field-effect transistors (FETs).
 38. The system of claim37, wherein the switches are coupled to the first battery cell in anH-bridge configuration.
 39. The system of claim 28, wherein the stackcontroller sends command signals to a first stage and a last stage ofthe battery stack.
 40. The system of claim 28, further comprising asecond isolator coupled between a last stage of the battery stack andthe stack controller, wherein the stack controller receives commandsignals from the last stage in the battery stack.
 41. The system ofclaim 28, further comprising the battery stack comprising the pluralityof stages, wherein the plurality of stages comprises: the first stagecomprising the first, battery cell; and the second stage comprising thesecond battery cell.